We are requesting funds to purchase a new Beckman Optima XL Absorption Analytical Ultracentrifuge to replace an obsolete and no longer serviceable unit which we have been unable to use for the past three years (Beckman "Model E" ultracentrifuge). The Principal Investigator has many years of experience in the use of the unit and will be responsible, with the assistance of Dr. Gunther Fless, for its maintenance and smooth performance. The ultracentrifuge will be housed in the NHLBI Shared Research Facility (SRF) at the University of Chicago which is directed by the P.I. The administrative requirements of operating and maintaining the unit will be facilitated by the aid of an Internal Advisory Sub-committee which will work under the umbrella of the SRF's existing administrative structure and its advisory committees. The Sub-Committee will insure the use of the ultracentrifuge among qualified investigators on a shared basis inclusive of students and post-doctoral fellows for whom appropriate training will be provided. Operational and maintenance costs will be shared among the users under the overall supervision of the Biological Sciences Division.